• Explosives and Blasting
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• v.35 no.3
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• pp.31-54
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• 2017

In the countries operating nuclear reactors, the development of high-level radioactive waste(HLW) disposal technique is considered as an urgent and important issue for sustainable utilization of nuclear energy. In Korea, in which a low and intermediate radioactive waste repository is already operating, the construction of an underground research laboratory for in situ validation studies became a matter of interest with increasing concerns on the management of HLW. In order to construct and to operate an underground HLW repository safely in deep underground, the stability of rock mass should be guaranteed. As an important factor on rock stability, excavation damaged zone (EDZ) has been studied in many underground research laboratories in foreign countries. For accurate evaluation of the characteristics and effects of EDZ under disposal condition, it is required to use reliable investigation method based on the analysis of previous studies in similar conditions. In this study, status of foreign underground research laboratories in other countries, approaches for investigation the characteristics, size, and effect of EDZ, and major findings from the researches were surveyed and reported. This will help the accomplishment of domestic researches for developing HLW management techniques in underground research laboratory.

• Journal of Radiation Protection and Research
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• v.31 no.1
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• pp.37-46
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• 2006

For the first step to develop a reference disposal container of spent fuel to be used in a deep geological repository, this paper examined safe dimensions of the disposal container on the points of nuclear criticality and radiation safety and mechanical structural safety and provided basic information for dimensioning the container and configuration of the container components, and establishing the favorable and safe disposal conditions. When the safety factor for stress due to the external loads (hydrostatic and swelling pressure) is taken as 2.0, the safe diameter of the filler material to provide enough container strength under the assumed external loads is found to be 112cm with 13cm spacing between inner baskets in PWR container. Also the thickness of the thinner section between the fuel basket and the surface of the cast insert is determined to be 150 mm. Regarding these dimensions of the container, the PWR fuel container is sketched to accommodate 4 square assemblies or 297 CANDU fuel 297 bundles (33 circle tubes x 9 stacks). However the top and bottom parts need to be checked again through the detail radiation shielding analysis with respects to the emplacement position and handling processes of the disposal container.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.20 no.4
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• pp.427-433
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• 2007

A structural model of the spent nuclear fuel disposal canister for the pressurized water reactor(PWR) for about 10,000 years long term deposition at a 500m deep granitic bedrock repository has been developed. However this developed structural model of the spent nuclear fuel disposal canister is too heavy to handle without any structural safety problem. Hence a lighter structural model of the spent nuclear fuel disposal canister which is easy to handle has been tried to develop very much. One of the reasons which made the structural model heavy is considered to be due to the severe adaptation of the design conditions like external loads and safety factor etc. to the canister design. Hence a complementary analysis to alleviate such severe design conditions is required for the reduction of the canister weight. In this study, a complementary structural analysis for the spent nuclear fuel disposal canister is carried out changing the design conditions such as external loads and safety factors to recalculate the design parameters like diameter and thickness etc. of the canister. The complementary analysis results shows that the diameter of canister can be shortened from 122cm to 102cm to reduce the weight of the spent nuclear fuel disposal canister.

• Economic and Environmental Geology
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• v.56 no.5
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• pp.515-532
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• 2023

Bentonite, predominantly consists of expandable clay minerals, is considered to be the suitable buffering material in high-level radioactive waste disposal repository due to its large swelling property and low permeability. Additionally, the bentonite has large cation exchange capacity and specific surface area, and thus, it effectively retards the transport of leaked radionuclides to surrounding environments. This study aims to review the thermodynamic sorption models for four radionuclides (U, Am, Se, and Eu) and eight bentonites. Then, the thermodynamic sorption models and optimized sorption parameters were precisely analyzed by considering the experimental conditions in previous study. Here, the optimized sorption parameters showed that thermodynamic sorption models were related to experimental conditions such as types and concentrations of radionuclides, ionic strength, major competing cation, temperature, solid-to-liquid ratio, carbonate species, and mineralogical properties of bentonite. These results implied that the thermodynamic sorption models suggested by the optimization at specific experimental conditions had large uncertainty for application to various environmental conditions.

• Explosives and Blasting
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• v.41 no.3
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• pp.38-61
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• 2023

An Excavation Damaged Zone(EDZ) caused by blasting impact changes rock properties, in situ stress distribution, etc., and its effects are noticeable at around a radioactive waste repository located at deep underground. In particular, the increase in permeability due to the formation of cracks may significantly increase the amount of groundwater inflow and the possibility of radioactive nuclide outflow. In this study, FLAC2D and FLAC3D were used to analyze the mechanical and thermal behaviors for three categories: a)No EDZ, b)Uniform EDZ, and c)Random EDZ. It was found that the tunnel displacement in the Random EDZ case was 423% higher than that in the No EDZ case and was 16% higher than that in the Uniform EDZ case. Tunnel inflow in the Random EDZ was also 17.3% and 10.8% higher than that in the No EDZ and the Uniform EDZ case, respectively. The permeability around the tunnel was increased by up to 10 times in the corner of the tunnel wall and roof due to the stress redistribution after excavation. From the computer simulation, it was found that the permeability around the tunnel wall was partially increased but the overall tunnel inflow was decreased with increase of stress ratio. Mechanical analysis using FLAC 3D showed similar results. Slight difference between 2D and 3D could be explained with the development of plastic zone during the advance of tunnel excavation in 3D.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.14 no.4
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• pp.515-523
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• 2001

In this paper results of a linear structural analysis for design and dimensioning of disposal containers for spent pressurized water reactor nuclear fuel and spent Canadian deuterium and uranium reactor nuclear fuel are presented. The container structure studied here is a solid structure with a cast insert and a corrosion resistant outer shell, which is designed for the spent nuclear fuel disposal in a deep repository. An evenly distributed load of hydrostatic pressure from the groundwater and large swelling pressure from the bentonite buffer are applied on the container. Hence, the container must be designed to endure these large pressure loads. In this study, the array type of inner baskets and thicknesses of outer shell and lid/bottom are attempted to be determined through a linear static structural analysis.

• Geomechanics and Engineering
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• v.16 no.4
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• pp.363-373
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• 2018

The evaluation of Thermo-Hydro-Mechanical (THM) coupling behavior is important for the development of underground space for various purposes. For a high-level radioactive waste repository excavated in a deep underground rock mass, the accurate prediction of the complex THM behavior is essential for the long-term safety and stability assessment. In order to develop reliable THM analysis techniques effectively, an international cooperation project, Development of Coupled models and their Validation against Experiments (DECOVALEX), was carried out. In DECOVALEX-2015 Task B2, the in situ THM experiment that was conducted at Horonobe Underground Research Laboratory(URL) by Japan Atomic Energy Agency (JAEA), was modeled by the research teams from the participating countries. In this study, a THM coupling technique that combined TOUGH2 and FLAC3D was developed and applied to the THM analysis for the in situ experiment, in which rock, buffer, backfill, sand, and heater were installed. With the assistance of an artificial neural network, the boundary conditions for the experiment could be adequately implemented in the modeling. The thermal, hydraulic, and mechanical results from the modeling were compared with the measurements from the in situ THM experiment. The predicted buffer temperature from the THM modelling was about $10^{\circ}C$ higher than measurement near by the overpack. At the other locations far from the overpack, modelling predicted slightly lower temperature than measurement. Even though the magnitude of pressure from the modeling was different from the measurements, the general trends of the variation with time were found to be similar.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.14 no.4
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• pp.321-329
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• 2016

Based on the results of groundwater flow system modeling for a hypothetical deep geological repository site, quantitative and spatial distributions of groundwater flow rates at the positions of deposition holes, groundwater travel length and time from the positions to the surface environment were analyzed and used to suggest a method for determining locations of deposition holes. The hydraulic head values at the depth of the deposition holes and a particle tracking method were used to calculate the ground-water flow rates and groundwater travel length and time, respectively. From the results, an approach to designing a layout of deposition holes was suggested by selecting relatively favorable positions for maintaining performance of the disposal facility and screening some positions of deposition holes that did not comply with specific constraints for the groundwater flow rates, travel length and time. In addition, a method for determining a geometrical direction for extension of the disposal facility was discussed. Designing the layout of deposition holes with the information of groundwater flow at the disposal depth can contribute to secure performance and safety of the disposal facility.

• Nuclear Engineering and Technology
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• v.20 no.2
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• pp.120-131
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• 1988

A souce term model describes mathematically the source of radionuclides as they begin slow migration and decay in deep groundwater. Various source term models based on mass-transfer analysis and measurement-based source term models are reviewed. Ganerally, two processes are involved in leaching or dissolution: (1) chemical reactions and (2) mass transfer by diffusion. The chemical reaction controls the dissolution rates only during the early stage of exposure to groundwater. The exterior-field mass transfer may control the long term dissolution rates from the waste solid in a geologic repository. Mass-transfer analyses re3y on detailed and careful application of the governing equations that describe the mechanistic processes of transport of material between and within phases. If used correctly, source term models based on mass-transfer theory are valuable and necessary tools for developing reliable predictions.

• Tunnel and Underground Space
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• v.30 no.6
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• pp.519-539
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• 2020

We reviewed numerical approaches to assess a hydraulic properties of excavation-disturbed zone (EDZ)created in argillaceous sedimentary rocks. It has been reported that fractures in the sedimentary rocks containing expansive clays are gradually closing due to swelling and their permeabilities are evolving to the level of in-tact rock, which is known as a self-healing or self-sealing process. The numerical approaches introduced here are capable of simulating spatio-temporal variation of EDZ permeability during long-term operation of a repository by including the self-healing characteristics of fractures, which wa observed in laboratory as well as in-situ experiments, The applicability of the numerical approaches was verified from the comparison to in-situ measurements of EDZ permeability at underground research laboratories.